In the US your backyard isn't necessarily considered to have an expectation to privacy.

The principle in question is Curtilage, the relevant holding was United States v Dunn. http://en.wikipedia.org/wiki/Curtilage

The fence argument is interesting, the factors they'd need to consider are outlined in the Wiki article. It's also why a professor of mine who was a lawyer told us in DC that if we ever got a MPD citation for drinking in public on our porch that he'd take the case for free, as he felt the law would clearly be unconstitutional - and said he'd have fun doing it.

I've done a bit of googling on this myself, and all I can find is that evidence could be thrown out in a criminal case based entirely on aerial footage, but that is rarely the only evidence provided. You likely don't own the airspace above your property, certainly not above a thousand feet, and technically no one owns outer space, so I would say that in 2013 or beyond, your expectation of privacy in your back yard is likely to dwindle severely over time.

If Google Maps used the image, they'd have to blur your sunbathing.